Dishwashers having a heat exchanger

ABSTRACT

A dishwashing machine comprising a tub that defines a wash space where dishes can be washed, a sump fluidly connected to the tub, a drain pump fluidly connecting the sump to a discharge pipe, a water tank fluidly connected to the sump though an on-off value and a softener, a heat exchanger located inside the water tank, and a diverter valve.

TECHNICAL FIELD OF THE INVENTION

The present invention generally relates to the field of dishwashing appliances and more particularly to dishwashers of the type having a heat exchanger allowing to recover thermal energy from hot waste water.

BACKGROUND

It is known that energy consumption requirements of household appliances are becoming stricter and stricter, constantly leading manufacturers to look for improved solutions. In the case of dishwashing machines it is known to use hot water from a previous washing cycle phase as a heat exchange media to pre-heat fresh water stored in a tank or container and intended to be used for a subsequent washing cycle phase. In this way less thermal energy is needed to bring the fresh water to the temperature required to carry out the washing cycle, e.g. 65° C. DE3901169 gives an example of a dishwashing machine of this type.

SUMMARY OF THE INVENTION

The aim of the present invention is to provide a dishwashing machine with a heat exchanger that allows to improve energy savings compared to the solutions known in the art.

This aim is achieved by a dishwashing machine according to the independent claim 1. Preferred features of the present invention are set forth in the dependent claims.

A dishwasher according to the invention is provided with a fresh water tank or container inside which a heat exchanger brings hot waste water collected in a sump into thermal contact with fresh water fed by an external water supply. Thermal energy is thus transferred in the form of heat from the hot waste water to the fresh water before the hot waste water is drained out to an external discharge pipe. According to the invention, hot waste water is made to circulate through the heat exchanger by a drain pump of the dishwashing machine, which is fluidly connected to a diverter or directional valve. The diverter valve, which is driven by a control unit of the washing machine, may be set either in a first configuration, wherein fluid communication is established between the drain pump and the heat exchanger, or in a second configuration, wherein fluid communication is instead established with a discharge pipe and hot waste water is drained out.

Thanks to the relatively short flow path from the drain pump to the fresh water tank compared with the flow path between the latter and the wash pump of a dishwashing machine, losses of thermal energy are minimized, thus improving efficiency of the heat recovery process. For the same reason, the flow rate of the hot waste water made to circulate through the heat exchanger can be more accurate and stable, which allows to achieve a very good performance during the heat exchange process.

By using the drain pump as a means to recirculate waste water in addition to drain it, substantially no structural complexity is added to main washing circuit of the dishwashing machine, while the manufacturing costs are affected in a very limited way.

Since the main washing circuit is not affected by the heat recovery function, the dishwashing machine features a modular design allowing to easily create product variants.

According to one of such variants, a closed-loop drying circuit of the washing machine may advantageously be connected to the drain pump in parallel with the heat exchanger, thus allowing to exploit the same pump for supplying hot waste water to the heat exchanger, simply draining it, or for pumping fresh water received in the sump into a tank of the closed-loop drying circuit to cool a condenser thereof during the drying process.

Further advantages, features and operation modes of the present invention will become clear from the following detailed description of embodiments thereof, which are given for illustrative and not-limiting purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will be made to the figures of the accompanying drawings, in which:

FIG. 1 is a diagram schematically showing the main components of a dishwashing machine according to an embodiment of the present invention;

FIG. 2 is a diagram schematically showing the main components of a dishwashing machine according to another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference initially to FIG. 1, a dishwashing machine according to the invention is generally indicated by reference number 100. The dishwashing machine 100 comprises a tub 110 that is disposed in an outer case (not shown) and defines a wash space where dishes can be received for washing. A sump 120 is fluidly connected to the tub 110 to receive the wash water needed to wash dishes and to collect the wash water to be recirculated during a wash cycle. As schematically shown in FIG. 1, the sump 120 may be arranged e.g. under the tub 110 it in a vertical direction so as to collect water by gravity.

A door (not shown) of the washing machine opens or closes the tub 110. The door may be equipped with a control panel and an associated control unit (not shown) that control operation of the dish washing machine 100.

The tub 110 houses a plurality of racks (not shown) where dishes can be placed for washing. The racks may comprise e.g. a top rack and a bottom rack disposed under the top rack.

The tub 110 also comprises a plurality of spray arms (not shown), which are supplied with wash water from the sump 120 and spray it towards the dishes arranged on the racks disposed inside the tub 110. To this aim a wash pump (not shown) is employed.

The spray arms may comprise e.g. a bottom arm (not shown) connected to the sump 120, an intermediate arm (not shown) disposed above the bottom arm and supplied with the wash water from the sump 120, and a top arm (not shown) disposed above the intermediate arm and supplied with the wash water from the sump 120.

It will be appreciated that the configuration of the door and of the racks and spray arms arranged in the tub are not limiting features of the invention.

A drain pump 130 is fluidly connected to the sump 120 to discharge the wash water at the end of a wash cycle.

The dishwashing machine 100 also comprises a water tank 140, i.e. a container or reservoir, configured to receive and store a predefined amount of fresh water from an external water supply, e.g. the water mains. The water tank 140 is fluidly connected to the sump 120 through an on-off valve 141 and a softener 150. At the beginning of a wash cycle, the on-off valve 141 is opened and the fresh water stored in the water tank 140 is made to pass through the softener 150 and collected into the sump 120, where it is heated and made to circulate to the spray arms. The on-off valve 141 is configured to allow either to store water in the tank 140 as discussed above, or to let it pass directly from the main water supply to the softener 150 as it happens in prior art dishwashing machines.

The dishwashing machine 100 according to the invention also comprises a heat exchanger 160 that is arranged inside the water tank 140. The heat exchanger 160 may for instance be integrally formed with the water tank 140, or it can be made as a separate component housed in the water tank 140.

The heat exchanger 160 has an inlet 161 fluidly connected with the drain pump 130 via a diverter valve 131 and a pipe, as well as through an outlet 162 that is fluidly connected to the tub 110.

At the end of a wash cycle phase the diverter valve 131 connected to the drain pump 130 allows to selectively supply the hot waste water collected in the sump 120 to the heat exchanger 160 so as to warm fresh water stored in the water tank 140. For instance, the cycle phase can be the main wash phase, wherein a detergent is dispensed into the tub.

Hot waste water enters the heat exchanger 160 at the inlet 161 and is discharged through the outlet 162 back into the tub 110, from which it reaches the sump 120 and may be made to recirculate into the heat exchanger 160. The thermal energy of the hot waste water collected in the sump 120 at the end of a wash cycle can thus be transferred to the fresh water stored in the water tank 140 before the waste water is discharged from the dishwashing machine by the drain pump. To this aim, the diverter valve 131 is set in fluid communication with an external discharge pipe, thus interrupting fluid communication with the heat exchanger 160.

In other words, according to the invention hot waste water, which is drained out of a prior art dishwashing machine, is instead effectively used at the end of a wash cycle phase in order to recover thermal energy to heat the fresh water stored in the water tank 140. A subsequent washing cycle phase will therefore benefit from pre-heated water, whose temperature is the ambient temperature or higher, thus requiring a lower amount of thermal energy to reach a desired temperature. For example, hot water having a temperature of about 50° C. is typically required in the rinsing phase. By making hot waste water, which has a temperature of about 45° C., to flow through the tank 140 the thermal energy needed to heat fresh rinsing water stored therein is much lower than the energy that would be required to heat it directly from the water supply. Energy consumption is therefore effectively reduced.

The diverter valve 131 is automatically controlled by the control unit of the dishwashing machine 100.

The arrows in FIG. 1 schematically show the path of the water flow in the different parts of the dishwashing machine 100, in particular from the drain pump 130 to the heat exchanger 160 and the tub 110, as well as from the tank 140 to the softener 150 and to the sump 120.

Thanks to the relatively short flow path from the drain pump 130 to the fresh water tank 140 compared to the typical length of the flow path between the same tank and the wash pump of a dishwashing machine, losses of thermal energy from the hot waste water are minimized, thus improving efficiency of the heat recovery process. For the same reason, the flow rate of the hot waste water made to circulate through the heat exchanger 160 is more accurate and stable, which allows to achieve a very good performance during the heat exchange process.

Moreover, the electric motor driving the drain pump 130 may advantageously be smaller than the motor of the wash pump, which contributes to increase energy savings during operation of the dishwashing machine. The drain pump 130 preferably has a variable speed motor, which provides the further advantage of a low noise during operation.

During a typical wash cycle phase, fresh water stored in the water tank 140 is fed to the sump 120 via the softener 150 and used for a pre-wash step. No soap is generally used in this phase. The water tank 140 is then refilled from the external water supply.

The water used for the pre-wash step is drained by the drain pump 130 and the fresh water stored in the tank is filled to the sump 120, heated to a desired temperature, e.g. 65° C., and used to carry out the main wash cycle together with a measured amount of soap stored in a suitable reservoir of the dishwashing machine 100.

According to the invention, at the end of the heated main wash phase, fresh water is filled into the water tank 140 and the hot waste water collected in the sump 120 is made to circulate through the heat exchanger 160 by the drain pump 130 so as to recover thermal energy and heat the fresh water stored in the tank 140. As discussed above, the diverter valve 131 associated with the drain pump 130 is set in fluid communication with the heat exchanger 160. After this process the diverter valve 131 is set in fluid communication with a discharge pipe and the waste water is drained out.

The water tank 140 can further be used to store water from the very last rinse phase and use it in the pre-wash phase of the following wash cycle.

A subsequent wash cycle phase will therefore benefit from pre-heated water stored in the water tank 140. It will be appreciated that the pre-heated water is at room temperature or higher depending on the time that lapses between a wash cycle and a subsequent one.

Now referring to FIG. 2, according to another embodiment of the invention the drain pump 130 may advantageously be fluidly connected not only to the heat exchanger 160, but also to a closed-loop drying assembly of the dishwashing machine 100. Such an assembly is typically employed to remove moisture from hot air used to dry dishes after a wash cycle. The closed-loop drying assembly of the dishwashing machine 100 of the invention comprises in a known way a water tank 180 having an inlet 181 and an outlet 182 allowing to fill in and discharge water, respectively. According to the invention, the inlet 181 is fluidly connected to the drain pump 130, thereby allowing to use this pump to feed fresh water received in the sump 120 through the external water supply and the softener 150 to the water tank 180.

This results in further energy savings in view of the small power motor employed by the drain pump compared to the motor of the wash pump.

As shown in the embodiment of FIG. 2, the drain pump 130 is fluidly connected to the water tank 180 of the closed-loop drying assembly by way of a first diverter valve 131, which is the same valve described above in connection with the previous embodiment of the invention, and by way of a second diverter valve 132 arranged downstream of the first diverter valve 131 and connected in series with it. Both valves are automatically driven by the control unit of the dishwashing machine 100. According to this configuration, the first diverter valve 131 is configured to establish fluid communication with either the second diverter valve 132 or the external discharge pipe, while the second diverter valve is configured to establish fluid communication with either the heat exchanger 160 or the tank 180 of the closed-loop drying assembly.

The arrows in FIG. 2 schematically show the path of the water flow in the different parts of the dishwashing machine 100, in particular from the drain pump 130 to the heat exchanger 160 and the tub 110, as well as from the tank 140 to the softener 150 and to the sump 120. The water flow path to the water tank 180 of the closed-loop drying assembly is also schematically shown.

It will be appreciated that a single three-way valve might be used instead of the first and second diverter valves described above.

Considering that the fresh water stored in the water tank 180 and used to cool the condenser during the drying cycle is at least at room temperature, an additional water amount is available to be fed to the sump 120 and employed in a wash cycle together with the water stored in the water tank 140 associated with the heat exchanger 160. To this aim an on-off valve 183 may be arranged downstream of the outlet 182 and connected in series with the water tank 180 of the closed-loop drying assembly.

According to this configuration the water stored in the water tank 140 having the heat exchanger 160 may be used e.g. for a pre-wash step. As discussed above, this water is at least at room temperature. The fresh and clean water stored in the water tank 180 of the closed-loop drying assembly, which is also at least at room temperature, can be used for the main wash step. After the main wash step the resulting hot waste water can be fed to the heat exchanger 160 and used to warm fresh water newly fed from the water supply into the water tank 140, which may in turn be used for a final rinse step.

The present invention has hereto been disclosed with reference to preferred embodiments thereof. It will be appreciated that there may be other embodiments relating to the same inventive idea, all of which are included in the scope of protection defined by the claims set out below. 

1-8. (canceled)
 9. A dishwashing machine comprising: a tub that defines a wash space where dishes can be washed; a sump fluidly connected to said tub; a drain pump fluidly connected to the sump to discharge waste wash water at the end of a wash cycle; a water tank configured to receive and store a predefined amount of fresh water from an external water supply, said water tank being fluidly connected to the sump through an on-off valve and a softener; a heat exchanger arranged inside the water tank; wherein said heat exchanger has an inlet fluidly connected with the drain pump and an outlet fluidly connected to the tub; and wherein a diverter valve is arranged downstream of the drain pump and configured to selectively direct a flow of water coming from the drain pump to either the heat exchanger or an external discharge pipe.
 10. The dishwashing machine of claim 9, further comprising a closed-loop drying assembly having a water tank with an inlet and an outlet, and wherein the drain pump is also fluidly connected to said inlet to selectively supply water to the water tank, while said outlet is fluidly connected to the sump.
 11. The dishwashing machine of claim 10, wherein the drain pump is fluidly connected to the water tank through a first diverter valve and a second diverter valve arranged downstream of the first diverter valve and connected in series with it, said second diverter valve being fluidly connected to the inlet of the heat exchanger and to the inlet of the water tank of the closed-loop drying assembly.
 12. The dishwashing machine of claim 10, wherein an on-off valve is associated with the outlet of the water tank of the closed-loop drying assembly, said on-off valve being operable to selectively feed water from the water tank to the sump.
 13. A method to operate a dishwashing machine having a heat exchanger arranged inside a water tank configured to receive and store a predefined amount of fresh water from an external water supply, said method comprising the following steps: feeding fresh water stored in said water tank to a sump of the dishwashing machine via a softener; heating the fresh water received in the sump at a desired wash temperature; carrying out a wash cycle; filing fresh water into the water tank; making hot waste water collected in the sump at the end of the wash cycle to circulate through the heat exchanger; and draining the waste water out of the dishwashing machine; wherein a drain pump of the dishwashing machine is employed to make the hot waste water circulate through the heat exchanger.
 14. The method of claim 13, wherein a diverter valve arranged downstream of the drain pump is employed to selectively supply hot waste water to the heat exchanger.
 15. The method of claim 13, wherein the drain pump is also fluidly connected with a water tank of a closed-loop drying assembly of the dishwashing machine, and wherein after the wash cycle the drain pump is employed to supply fresh water to said water tank to cool a condenser of said closed-loop drying assembly.
 16. The method of claim 15, wherein an on-off valve is associated with an outlet of the water tank of the closed-loop drying assembly, and wherein said valve is operated to selectively feed the water supplied by the drain pump to the water tank to the sump.
 17. A dishwashing machine comprising: a tub defining a wash space where dishes can be washed; a sump fluidly connected to the tub; a drain pump fluidly connecting the sump to a discharge pipe; a first water tank fluidly connected to the sump through a first on-off valve and a softener; a heat exchanger located inside the first water tank, the heat exchanger having a heat exchanger inlet and a heat exchanger outlet fluidly connected to the tub; and a first diverter valve selectively fluidly coupling the drain pump to the heat exchanger inlet or the external discharge pipe.
 18. The dishwashing machine of claim 17 further comprising a closed-loop drying assembly having a second water tank with a second water tank inlet fluidly connected to the drain pump, and a second water tank outlet fluidly connected to the sump.
 19. The dishwashing machine of claim 18 further comprising a condenser located inside the second water tank of the closed-loop drying.
 20. The dishwashing machine of claim 18 further comprising a second diverter valve, downstream of the first diverter valve, selectively fluidly coupling the drain pump to the heat exchanger inlet or the second water tank inlet.
 21. The dishwashing machine of claim 20 wherein the second diverter valve is connected in series with the first diverter valve.
 22. The dishwashing machine of claim 18 wherein the second water tank outlet is fluidly connected to the sump through a second on-off valve.
 23. A method of operating a dishwashing machine having a heat exchanger arranged inside a water tank configured to receive and store a predefined amount of fresh water from an external water supply, the method comprising: feeding fresh water stored in the water tank to a sump of the dishwashing machine via a softener; heating the fresh water received in the sump to a desired wash temperature; carrying out a wash cycle; collecting hot waste water in the sump at an end of the wash cycle; circulating the hot waste water with a drain pump through the heat exchanger; and draining the waste water out of the dishwashing machine.
 24. The method of claim 23 further comprising selectively supplying the hot waste water to the heat exchanger via a first diverter valve downstream of the drain pump.
 25. The method of claim 24 further comprising supplying fresh water with the drain pump to a second water tank having a condenser of a closed-loop drying assembly located therein.
 26. The method of claim 25 further comprising selectively feeding the water supplied by the drain pump to the second water tank, to the sump via an on-off valve. 